In principle, the matrix elements \(C_{ij}\)  contain full information of the cross-correlations between stocks,
but carry also strong noises.
To sketch the backbone of the interactions between stocks, the edges should be greatly discarded with
respect to the complete graph. To this aim, the graph should be kept as simple as possible, but
important correlations should remain. The MST tree
is therefore the
simplest connected graph [1]}, [2]}, in which there are no cycles. Moreover, the MST tree may give
the simplest subdominant organization structure of individual stocks in a direct scheme.
